Optical glass



Dec. 6, 1949 w. H.AR M|sTEAD 2,490,331

OPTICAL GLASS Filed Nov. 9, 1945 Qttutneys Patented Dec. 6, 1949 uNrrli-e STATES omar.

2,496.33` OPTICAL GLASS H. -Atlmsteadi Corn'ng, N, UY.,I assignormtg v Corning Glass Works;V Cohing`-,"`N:"Y.,"a-cor" poration of New York This' invention relates tcioptical glasses and dex (u). This combination' ofoptical'properties' makes the barium crowns veryuseful for the production of lenses" of' var'iiiskinds.

For some purposes it is desirable to use glasses having higher refractive indices; upto about 1.8, and also havingI high dispersive indices'. The

refractive index of barium crowr'i-"gla'sses'hasbeen limited to a maximum of about 1.63 because an increase in the barium content beyond this point, about 50% BaO, results in devitrification of the glass when-it is slowly cooled or reheated for molding. n l Y The primary'ob'jct"ofth'is invention is to pro-4 vide transparent optical glasses-,which have refractive indices (nn) greater than 1.64 together with high dispersive indices*(1)); n

An'ot-herobjecteis to f'pvide* barium i crown glasses which -contain over-550%'ian`d up'to "70% BaO and which will not devitrify when reheated or slowly cooled.

Another object is to prevent; the devitrication of barium crown glasses having barium contents above 50% BaO.

Another object is to provide glasses which have refractive indices greater than 1.64, and preferably greater than 1.675 and correspondingly high dispersive indices, and which contain a ttal of at least 60%, and preferably at least 65% BaO and PbO.

I have found that the introduction of substantial percentages of lead amounting to at least 5% PbO into dense barium crown glasses prevents devtriflcation of the glass whereby the barium content can be increased to as much as about 70% BaO with a corresponding gain in refractive index, provided that the glass also contains substantial B203, S102, and preferably at least one of the refractory oxides A1203 or Zr02. The introduction of PbO also tends to raise the refractive index of the glass and does not lower the dispersive index objectionably, provided that the barium content is at least 50% BaO. For the accomplishment of my purpose it is necessary that the total BaO and Pb0 be at least 60%.

I am aware that glasses containing both BaO and PbO have heretofore been made as optical glasses and for other purposes, but such prior glasses do not contain more than about 40% BaO, at the most and do not have the desirable op (o1. messe) tial properties" of,` new ,gl-asses.`" Moreover,

o"'l'n'vowri"` that the barium cons inc sedbzeyoiid"50%BaO- without devitiicationwhenatleast 5 of PbO'is present. In-'rriyv co-pe'n'dingvapplication',v Serial Number'62`7g746 filed'j concurrently herewith,l I have df'opticalgl'assesfhaving'high M `high`dis1ersiv indicesY and iid- CQOQQ It' is therein shown that thein y'tio'n -ofCdO not'only 'prevents devitricatiprlof the; glass but also is of benetfolnrofiu" a high reirativeindex and `.Tl'ie'v'g'lafsses'of thepresent invention are- Adis'tinguis hed fromk fthe" glassesof \dir'ig'-"a;1plicationfirr that the present rd'ance with '1; he''ol`oj`'zctsfoffthe present iiventionytli glassesshouldticontain' from 2 to e/-offsi'oz"aridfrA '5% @fsw-'1320315 Prefer- 25s ably they should'lals'o contairiAlzOs or ZrOz', or

both. The A1203 aidsjin preventing devitriiication and may arrfuntil?.fromA 1% @12% The Z'r02`ff being'les soluble Linaya'mountgto from 1 %""to 7 It 'a'lsiaids'in'preventing ldvitrii-lca- 25 tion and also helps to raise both the refractive index and the dispersive index. Although not particularly desirable, small percentages of the alkali metal oxides (R20) and other oxides which are commonly used in optical glass compositions such as Be0, CaO, SrO, ZnO, A5203, SbzOa, TiOz, etc., may also be included in the new glasses but preferably should not exceed a total of about 5%.

The following glasses, which are given in percent by weight as calculated from their respective batches, show by way of example compositions which I have melted and which fall within the scope lof my invention:

The above glasses are chemically stable and resistant to devitrification. It will be noted that they have refractive indices falling within the range of 1.64 to 1.80 and relatively high dispersive indices. Glasses B, C, D and E are particularly suitable for my purpose.

To illustrate the relationship between nD and v for the glasses of this invention, reference is had to the accompanying drawing which is a diagram representing the values of 11D for the above glasses plotted against their respective values of u and designated by the letters of the respective glasses. It will be noted that the values for the various glasses are above the line X which represents the approximate minima in the values for nn and u which characterize the glasses of this invention.

The line X is drawn through the points (ny- 1.65, u=50) and (nD=1.75, u=35 and is defined by the equation I claim:

1. A transparent cadmium-free optical glass which contains 50% to 70% BaO, 5% to 30% Pb0, 2% to 25% S102 and 5% to 37% B203, the sum of which is more than 95% of the total composition, the total BaO and Pb being not less than 60%, and which has an index of refraction for the D line (11D) of at least 1.64 and a dispersive index (u) greater than v=297.5150 'n.D.

2. A transparent cadmium-free optical glass which contains 50% to 70% BaO, 5% to 30% PbO, 2% to 25% Si02, 5% to 37% B203, and 1% to 12% A1203, the sum of which is more than 95% of the total composition, the total BaO and PbO being not less than 60%, and which has an index of refraction for the D line (nn) of at least 1.64 and a dispersive index (v) greater than 3. A transparent cadmium-free optical glass which contains 50% to 70% BaO, 5% to 30% Pb0, 2% to 25% SiOz, 5% to 37% B203 and 1% to 7% Zr02, the sum of which is more than 95% of the total composition, the total BaO and PbO being not less than 60%, and which has an index of refraction for the D line (nu) of at least 1.64 and a dispersive index (u) greater than 4. A transparent cadmium-free optical glass which contains 50% to 70% BaO, 5% to 30% PbO, 2% to 25% Si02, 5% to 37% B203 and 1% to 12% A1203 and 1% to 7% Zr02, the Sum of which is more than 95% of the total composition, the total BaO and PbO being not less than 60%, and which has an index of refraction for the D line (nD) of at least 1.64 and a dispersive index (u) greater than v=297.5-150 nD.

5. A transparent cadmium-free optical glass which consists of to 70% BaO, 5% to 30% PbO, 2% to 25% SOz, 5% to 37% B203 and 1% to 12% A1203, the total BaO and Pb0 being not less than and which has an index of refraction for the D line (nn) of at least 1.64 and a dispersive index (u) greater than 6. A transparent cadmium-free optical glass which consists of 50% to 70% BaO, 5% to 30% Pb0, 2% to 25% S102, 5% to 37% B203 and 1% to 7% ZrOz, the total BaO and PbO being not less than 60%, and which has an index of refraction for the D line (nD) of at least 1.64 and a dispersive index (u) greater than u=297.5-150 11D.

7. A transparent optical glass which consists of approximately 9% Si02, 60% BaO, 10% PbO, 17% B203 and 4% Zr02.

WILLIAM H. ARMSTEAD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED vSTATES PATENTS Number Name Date 1,513,923 Montgomery Nov. 4, 1924 2,297,453 Berger et al Sept. 29, 1942 FOREIGN PATENTS Number Country Date 388,118 Great Britain 1933 596,513 Germany 1934 

